Antenna Near-Field Probe Station Scanner

ABSTRACT

A miniaturized antenna system is characterized non-destructively through the use of a scanner that measures its near-field radiated power performance. When taking measurements, the scanner can be moved linearly along the x, y and z axis, as well as rotationally relative to the antenna. The data obtained from the characterization are processed to determine the far-field properties of the system and to optimize the system. Each antenna is excited using a probe station system while a scanning probe scans the space above the antenna to measure the near field signals. Upon completion of the scan, the near-field patterns are transformed into far-field patterns. Along with taking data, this system also allows for extensive graphing and analysis of both the near-field and far-field data. The details of the probe station as well as the procedures for setting up a test, conducting a test, and analyzing the resulting data are also described.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/499,982, filed Aug. 2, 2006, the entire disclosure of which is herebyincorporated by reference herein.

STATEMENT OF GOVERNMENT INTEREST

The invention described herein was made by civil servant employees ofthe United States Government, and a non-civil servant employee workingunder a NASA contract, and is subject to the provisions of Section 305of the National Aeronautics and Space Act of 1958, Public Law 85-568 (72Stat. 435; 42 U.S.C. 2457).

FIELD OF THE INVENTION

The present invention relates generally to a scanner device for themeasurement of miniaturized antennas using near-field signals. Moreparticularly, it relates to a probe station scanner for measuringnear-field radiated power performance of a miniaturized antenna, and fortransforming the measurements into far-field characteristics.

RELATED ART

Before an antenna can be used for a particular application, the antennamust first be tested to determine its performance characteristics. Onecharacteristic, the radiation pattern, is generally tested in an antennarange. Antenna range types are numerous, and the choice of range to useis dependent on many factors. Antenna size, frequency of operation,mechanical supporting requirements and the intended application are buta few of the factors. For example, an electrically large antenna thatmust be tested indoors, requires the use of a near-field scanning range.Alternatively, a similar, but electrically smaller antenna may be ableto utilize a far-field range. Smaller yet, miniaturized antennas imposeadditional requirements not addressed by the conventional ranges andhence require a new approach.

Space exploration systems require the use of miniaturized antennas forsurface networks and planetary exploration communication. In addition,miniaturized antenna systems find use in cellular telephones, variouswireless connections, and a variety of embedded medical circuits fordiagnostics and treatment. Generally, a large number of these antennasare produced on a single wafer much like semiconductor devices. Probestations, used for semiconductor device characterization, can also beused to obtain antenna patterns when the devices are antennas. Doing soallows the antennas to be tested on wafer enabling a number ofadvantages over a more conventional technique. Conventionally theantennas must be separated using a procedure that is very time consumingand expensive. Then the single antenna must be placed in a fixture fortesting. The antenna must be isolated from the fixture, or the fixturewill adversely effect the characterization. Accordingly, theconventionally tested results do not always produce the true radiationpattern of the antenna.

BRIEF DESCRIPTION OF THE INVENTION

To facilitate the understanding of the present invention, theseabbreviations will have the following definitions, unless otherwiseprovided within this document.

AUT antenna under test

CPU central processing unit

CW continuous wave

DC direct current

FFT fast Fourier transform

Gain amplification factor; a boost in signal strength

G-S-G ground-signal-ground

GUI graphical user interface

MEMS micro electro-mechanical system

RF radio frequency

VNA vector network analyzer

This invention provides the capability for characterizing miniaturizedantennas while biasing any necessary active (e.g., MEMS) devices. Thisis conducted by measuring the near-field patterns of small micro-channelpatch antennas. Each antenna is excited using a probe station systemwhile a waveguide scans the space above the antenna to measure thenear-field signal. Upon completion of the scan, the near-field patternsare transformed into far-field patterns. Along with taking data, thissystem also allows for extensive graphing and analysis of both thenear-field and far-field data. The procedures for setting up a test,conducting a test, and analyzing the resulting data are also described.

The invention comprises a near-field probe station and its use forscanning the near-field radiated pattern of a miniaturized printedcircuit antenna. The probe station comprises a three axis probe slideand rotation platform. A coplanar waveguide and RF probe are mounted tomove along the three axes to provide input signals to the antenna undertest. The station may also include a DC probe to apply a DC bias to theantenna being tested. A network analyzer such as an HP8510C and acomputer are also included. A software program is usable with thecomputer for the analysis of near-field data collected with the scanner.This program is capable of displaying three dimensional contours of thefar-field pattern distribution of the antenna.

The invention also includes a software system for capturing thenear-field signals from a miniature antenna and for characterizing theactual behavior of the antenna based upon the captured signal. Thissystem comprises a management software package having the keyed-incapability of calling up other software packages embedded therein. Italso includes two embedded software packages. The first package isuseful in making a near-field to far-field transform. The second packageis a visual package having the capability of showing three dimensional,contours, vertical cuts and horizontal cuts through the far-fieldpattern distribution of the antenna.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings as described herein are presented for the purpose ofillustrating the invention, and its environment, and are not intended toserve as a limitation on the invention.

FIG. 1 is a flowchart of a computer program for characterizing miniatureantennas;

FIG. 2 is a schematic of the antenna scanner;

FIG. 3 is a layout showing the hardware components of the presentinvention;

FIG. 4 shows a panel for control of the operation of the scanner;

FIG. 5 is a three-dimensional graph of a near-field magnitude plot;

FIG. 6 is a near-field phase plot;

FIG. 7 is a far-field transform of the data shown in FIGS. 4 and 5;

FIG. 8 shows contour plots of the Far Field Magnitude; and

FIG. 9 is a top view showing multiple antennas on a single wafer.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to antenna metrology hardware fornon-destructive characterization of miniaturized passive or activeantennas fabricated on substrates (e.g., Gallium Arsenide (GaAs),Silicon (Si), Lanthanum Aluminate (LaAlO₃, etc.) which are difficult tomeasure in traditional ranges because of their smaller size, fragility,and non-trivial DC biasing or complicated fixturing requirements. Forthe purposes of the present invention, miniaturized antennas are thosehaving a dimension of about 1 cm or less, down to 1 mm or even smaller.Stated differently, these small antennas have a cross sectional size ofabout ⅕ to about ½ lambda, whereas large antennas have a size greaterthan ½ lambda. The scanner consists of a precision mechanical slidesystem, software analysis features, a probe station, and an automaticnetwork analyzer. The turn-key antenna near-field data acquisitionsystem in this scanner is extremely fast, automated, and user friendly.It only requires user information to be entered via soft-keys into theinput control panel.

Other functionalities of the invention include report-quality imagestorage for publication purposes, accessible data files for furtherfuture processing, and text documentation associated with each datafolder describing the test parameters and test conditions. Compared toother conventional ranges, this scanner offers considerable costsavings, reduces prototype characterization time from months to days,does not require a separate stand-alone data analysis and graphicvisualization platform, and is particularly suitable forcharacterization of miniature antennas.

A simplified flowchart of the computer program for controlling thevarious functional features of the invention is shown in FIG. 1. A scanis started at 10 by inputting a command from a computer keyboard. In thefirst step (12), the computer establishes a communication link with ascanning probe (described in the flow sheet as a waveguide probe) andwith the ground surface ground (G-S-G) microwave probe at the probestation. In the second step (14), a rectangular matrix of grid pointsfor the near-field data acquisition is provided to the probe station. Instep 3 (16), an RF signal is applied to the AUT through the G-S-G probe.Also, to the extent required, a DC bias is applied at 18 to any biaspads on the ALIT through the DC probe. Step 4 activates the 3-axis probeslide and probe rotation device at 20 to move the device to the variousgrid points established in Step 2 to record data at each point. In step5 (22), the computer controls the collection, analysis and visualizationof the data collected in Step 4. In step 6 the data is converted ortransformed (24) by the use of a FFT into the actual far-field pattern.

The invention features software which accesses commercially availablesoftware codes such as LabVIEW, Visual Basic, and Matlab to analyze themeasured near-field data to be able to display far-field antennapatterns either in 3-dimensional, contour form, or as vertical orhorizontal cuts through the antenna's far-field pattern distribution.LabVIEW is a graphical programming software tool available from NationalInstruments. Visual Basics is a tool to aid in the development of a widerange of applications based upon the NET framework, and is availablefrom Microsoft. MATLAB is a matrix algebra software package thatutilizes various algorithms for numerical experiments, graphics andcalculations. It is available through The Mathworks, Inc.

Space exploration systems require miniaturized antennas for surfacenetworks and planetary exploration communication. Thus, for design andoptimization of prototype antenna candidates for these uses, aneffective, fast, and reliable characterization capability is required.The near-field probe station scanner of the present invention providesnon-destructive characterization of small passive and active antennas,fabricated on semiconductor and, or dielectric wafers (e.g., GaAs, Si,LaAlO₃, etc.).

The near-field probe station scanner includes a near-field dataacquisition feature that allows for maximum power capturing andtherefore is very suitable for characterizing miniature antennas withlow gain. This capability allows the characterization of prototypeantennas, either of a single design, multiple variants of one design, ormultiple antenna designs on the same substrate in one session. This isachieved without the requirement for dicing or packaging of thesubstrate, and no test fixtures are necessary. Maximum near-field energycan be captured from a single or a multiple number of small antennaswhile they are DC biased without requiring a special fixture. RF signaland DC bias to the AUT are applied through the probe station RF and DCprobes. Multiple measurements and characterizations can be accomplishedin hours or days instead of months as with conventional ranges. Thus,this measurement capability significantly reduces time and costsassociated with antenna characterization, and allows for quickoptimization of prototype design concepts through measurementvalidation.

The schematic of FIG. 2 shows a platen 30 on which an AUT 32 is mounted.A waveguide probe 34 is positioned above the AUT and is for movementwithin the scan plane 36 in accordance with instructions that arereceived from the VNA 38. The VNA receives data from the AUT 32 andcommunicates with the CPU 40.

Turning next to FIG. 3, additional details of the hardware of thepresent invention are shown. In particular, a DC probe 42 is connectedto the VNA 38 and provides a DC bias to any bias pads on a transmittingAUT. The implementation of the present invention requires a RF probestation, a coplanar waveguide ground-signal-ground (G-S-G) microwaveprobe 44, and a scanning probe 34 such as an open ended waveguide probe.The RF probe station is available from sources such as CascadeMicrotech, Inc, Signatone Corporation and J micro Technology, Inc. G-S-Gprobes are made by GGB Industries, Inc., The Micromanipulator Company,and Lake Shore Cryotronics, Inc. Scanning probes such as waveguideprobes are available from sources such as Nearfield Systems, Inc,Agilent Technologies, Inc and Maury Microwave Corporation. A computercontrolled 3-axis probe slide and probe rotation mechanism provides 4degrees of freedom for data acquisition at described grid points of anear-field plane very close to the AUT and at different polarizations.This mechanism comprises an X-axis actuator 46, a Y-axis actuator 48, aZ-axis actuator 50, and a rotator 52. A vector networkanalyzer/microwave receiver 38 (such as a HP8510C) and a computer 40complete the system. Software controlled data analysis and visualizationafter each scan is achieved through a GUI which displays the AUT'sfar-field radiated pattern. Compared to prior art scanners, thisnear-field scanner offers much faster antenna measurements at a fractionof the cost.

The LabVIEW control panel is shown in FIG. 4 and consists of a window tojog the probe, enter appropriate scan parameters, and see initial testdata which can be viewed and analyzed later through the methods to beexplained infra. The top section is used for jogging the probe. The usercan enter the desired linear movement of the RF probe in millimeters, orthe rotation in degrees followed by clicking one of the eight movementbuttons corresponding to the four different axes to execute themovement. When the probe is jogged to a new position, this positionautomatically becomes the new Home position for the scanner. Whenrunning a scan, the Home position preferably is directly above thecenter of the intended scan area.

In certain circumstances the user may need to move the probe, but maywant to retain the current Home position. This can be accomplished withthe Freeze as Home button. When this button is selected no joggingcommand can reset the Home position. When this button is deselected theoriginal Home position will still be preserved until a jog is performedagain. The probe can be returned to the starting position at any timeoutside of performing a scan by selecting the Home button.

The top section of the panel also includes a Microscope button which isused to load an antenna onto the probe station's platen. The waveguideprobe must be moved out of the way to enable the microscope to be loadedonto the bridge mount to aid in biasing the antenna. When this button ispressed, the probe will be positioned to the far right corner of thelinear actuation range. This movement will not cause the Home positionto be reset. Pressing the Home button will reposition the probe to theposition it was in before the Microscope button was selected. If theprobe had not been positioned prior to pressing the Microscope button,then the Home position will not be defined by the user but by apredefined location hard coded into LabVIEW.

The section of the control panel below the jog portion of the panel isthe parameter portion. This section is located on the center of theLabVIEW panel. Here, the user must input all the important parametersfor the scan. The user should use caution when establishing the numberof data points and spacing to prevent crashing the probe with anyobjects that may be in the scan area. Every input must have an entryexcept for the Scan Comments text box. This is an optional input thatwill allow the user to record any important scan information to theExperiment_Parameters.rtf file.

At the bottom of the control panel is the status portion of the panel.Here, the user can monitor the progress of the scan, stop the scan, oranalyze the data after a scan is complete. When the Stop button isselected the scan will be abruptly stopped at the beginning of the nexthorizontal data point. If the program requires scanning the area twiceat 90-degree rotation shifts, then data will be saved for the firstshift if the Stop button is selected after the first scan shift.Otherwise, no data will be saved for that scan. The Graph & Analysisbutton will load a new window to allow the user to view and analyze datafrom current or previous scans, to be explained hereinafter.

For measurements, the AUT is first placed on the probe station platform.An RF signal is then applied to the AUT feed point through G-S-G probe,and DC bias to any bias pads on the AUT is applied through a DC probe.The near-field scan area dimension and the grid size resolution forprobe data intake are user defined in the control panel input. Probeslide hardware determines the scan area and number of measurement pointsfrom the user input. Once the probe is directed to move to the “home”position of the scan box, the scan process is started with a buttonclick. The RF probe auto traverses on the scan area and captures thenear-field power distribution from AUT at the grid points. Automateddata storage and multiple window graphic display allows patternvisualization capabilities in cross-sectional, 3-dimensional, andcontour formats for easy figure-of-merit comparison among designvariations and to quickly arrive at an optimized design.

Near-field data acquisition allows better power capturing capabilitiesand therefore is very convenient to characterize miniaturized antennaswith low gain. This new capability allows prototype antennas to becharacterized, either of a single design, multiple variants of onedesign, or multiple antenna designs on the same substrate, in onesession. FIG. 9 shows multiple antennas 32 a, b, c and d on a singularwafer 28, and mounted on a platen 30. Four G-S-G probes 44 are alsoshown, each with a signal probe 64 contacting the AUT. The two grounds56, 58 of each probe are joined to pads 60, 62 on the platform 28 onwhich the antennas are mounted.

Significant advantages of the present invention include 1) fast,turn-key, automated, user-friendly system, 2) elimination of waferdicing or packaging of individual antenna before characterization, 3)elimination of any test fixture or mounting scheme with specialconnector, launcher, or feed line transition, thereby reducing prototypeoptimization time and cost, 4) data analysis and graphic visualizationwithout requiring costly stand-alone platforms, and 5) extensive patternvisualization capability. The scanner system can be used for suchprograms as exploration missions in which it can accelerate thedevelopment and characterization of miniaturized antennas forlunar/planetary surface to surface communications.

Several other advantages of the invention are a) the scanner offers manyversatile viewing and data comparison options; b) the in plug-and-playmode features are unique with respect to other known antenna testranges; c) because miniaturized antennas are required for manyapplications (e.g. surface networks and planetary explorationcommunication), an effective, fast, and reliable characterizationcapability can be very timely in maintaining project timelines. Further,the technology can be used for applications such as evaluation ofminiaturized antennas for cellular telephones, and embedded medicalcircuits.

The present invention can be implemented in accordance with thefollowing summary of the procedure for preparing and calibrating thetest equipment, conducting the test, and then converting the near-fieldresults into more useful far-field data.

An S-parameter (e.g, S₁₁) calibration is performed with the VNA at theanticipated scanning frequency for the purpose of defining thescattering parameters of the system. The frequency range is limited bythe VNA and the availability of the scanning probe. The VNA isoperational from 45 MHz to 40 GHz, and the probes size will varyaccording the desired frequency, with the probe size decreasinginversely to frequency. Therefore, in principle the systems can beoperational within the aforementioned range. This calibration will helpensure the antenna is properly mounted and ready for scanning before thetest begins. In this example, the scanner is run using the LabVIEW code.

The waveguide probe is moved into a corner of the linear actuator so itdoes not interfere with a visual magnifier such as a microscope that maybe used for connecting the RF and DC probes to the antenna. The AUT isplaced onto the Probe Station's platen and is maintained in positionusing suitable means such as a vacuum system or other means that doesnot distort the AUT or alter its power distribution properties. The RFprobe is then placed on the antenna's feed port followed by any DCprobes that may be needed. The S₁₁ measurements are checked on the VNAto verify that the antenna is properly biased.

After the antenna is successfully biased, the microscope is removed andthe microscope mounting bracket is returned to the far back of the probestation to avoid contact with the probe during operation. Removing themicroscope and repositioning the bridge mount may cause movement andvibrations in the probe station. Accordingly, the S₁₁ parameters arerechecked to assure the antenna is still properly biased.

To prepare the scan, the waveguide probe is positioned directly over thecenter of the AUT. There are two different options for doing this. Theuser can either manually jog the probe from the position at the cornerof the linear actuator, or use a Home button on the computer keyboard.If the probe has been moved prior to centering, then it will return tothis original position. If the probe had not been moved prior tocentering, then the Home button will place the probe at a predefinedlocation hard coded into the computer program. Caution should beexercised when moving the waveguide probe to prevent crashing it intothe probe station. The probe is then centered over the AUT, at thedesired height and rotation for conducting the desired tests beforeproceeding.

After the probe is prepared, the following test parameters are keyedinto the computer. These parameters include:

Frequency—The single frequency at which the AUT will radiate (e.g., 2GHz) The equipment involved in the scan (waveguide, VNA, etc.) must becompatible with the set frequency used in the scan.

Delay—The time delay the probe should pause at each data position. Thedata are recorded 100 ms before the probe begins to move again. So for adelay of 1s, the data are measured and recorded 900 ms after stopping.If Delay is set to zero, a continuous scan is conducted.

Averaging—The number of data points averaged by the VNA for eachrecorded data point.

Ground Plane—Used in far-field calculations. Yes is chosen if the AUThas a ground plane. Otherwise, N is selected.

Cal Set—Allows the user to load a predefined Cal Set saved on the VNA.This Cal Set must be a CW calibration conducted directly on the VNA andmust coincide with the correct frequency entered in the LabVIEW Panel.If the Cal Set differs from the frequency being tested or is not CW, itwill be ignored by the scanner.

Polarization—Allows polarization of the AUT to be chosen. Thisdetermines the type of data that will be saved and how calculations aredone for the far field conversion.

FE Resolution—Used to determine the number of data points to be used inthe far-field conversion. Standard creates a far-field matrix of128×128, High creates a matrix of 256×256, and Very High creates amatrix of 512×512.

X axis Data Points—The number of data points along the x-direction thatshould be recorded during scanning. This number is typically an integervalue.

Y axis Data Points—The number of data points along the y-direction thatshould be recorded during scanning. This number should be an integervalue.

X axis Data Intervals—The interval spacing between x data points inunits of millimeters. This number can be a decimal value to thehundredths position.

Y axis Data Intervals—The interval spacing between y data points inunits of millimeters. This number can be a decimal value to thehundredths position.

Scan Comments—This text box allows the entry of any comments about thescan to be saved in the parameter text file.

Filepath—The file path of the data being saved. This data path mustspecify a folder in memory.

Filename—The File name of the data being saved. This Filename creates afolder that contains all the files created from the scan. The folderwill have the unique name for the scan, however, the files inside thefolder will be uniform across other scans.

When the test apparatus is properly set up, the scan begins by pressingthe Scan button. The probe positions itself over the Home position. Itthen proceeds to position itself at the location of the first datapoint. All scan lines are conducted across the x-axis. The status bargives an estimate of the progress for the scan.

When the scan is complete, the data is displayed in three graphs shownas FIGS. 5, 6 and 7. The Figures are shown in color to more accuratelydisplay the various slopes and contours portrayed in the graphs. Thegraphs are generally located on the right side of the LabVIEW panel. TheNear-Field phase and magnitude are typically displayed in the two smallgraphs, FIG. 5 and FIG. 6 respectively, shown on the monitor, while theFar-Field pattern is displayed in the larger graph (FIG. 7). Dependingon the polarization type, the scan may need to be conducted twice at 90degree rotation shifts. If two scans are required, the graphs will beupdated twice. After the first scan the near field magnitude and phaseare displayed in the two smaller graphs. If the scan is “CoPol andCrossPol” then the Co-Pol far-field is also be displayed for the firstscan. If the scan is circular no far-field pattern will be displayed.After the second scan, the new near-field magnitude and phase are thendisplayed along with either the circular far-field or updated Co-Pol farfield dependent on the type of polarization that is chosen. For moregraphing features, a “Graph & Analysis” button located in the statusportion at the bottom of the LabVIEW panel can be used.

The “Graph & Analysis” button opens a screen allowing the user to choosethe desired data folder. When a data folder is chosen, a display shows alist of different graphs available based upon the polarization of thescan within the data folder. The user may choose as many of the graphsto display before clicking the Open button. Each graph opens in its ownseparate window. This allows as many graphs to be viewed as required.The graphs can be resized by maximizing or dragging the window edges.The 2D graphs representing the H-cut and V-cut allow the user zoom in ona region of the graph. Double clicking on the graph will return thegraph to its original state. Future graphs can be opened from the Filemenu on each graph window. Each graph has the ability to be saved as abitmap file in the folder containing the scan data for later use. Thisis accomplished by clicking on Save as Image in the File menu. Eachgraph can also be printed from the File menu. The printed size isdetermined by the size the graph appears on the monitor. A full pageprintout can be obtained by maximizing the graph window and choosingPrint.

The Data Files

After each scan, a number of data files are saved to the scan folder.These files are matrices delimited by a tab and can easily be accessedusing a computer program such as Excel. The scan polarization determinesthe number and type of files saved in each scan folder. Each scan willcontain certain files. Those files include:

-   -   Graph_Parameters.gd—This is information needed for the graphing        feature. If this file is removed or altered the graphing        features in LabVIEW may not work.    -   Experiment Parameters.rtf—This is a text file saved in the “Rich        Text File” format. This file will display all the parameters        used when the scan was conducted along with any user comments        entered in the “comment box” before the scan.    -   theta.psd—The theta values corresponding to each far field data        point.    -   phi.psd—The phi values corresponding to each far field data        point.    -   u.psd—The u values corresponding to each far field data point.    -   v.psd—The v values corresponding to each far field data point.

Finally, the LabVIEW program generates the three graphs as shown inFIGS. 5, 6 and 7. The two near field graphs, FIGS. 5 and 6, areconstantly updated while data is being taken so the user can monitor theprogress and state of the data recorded thus far. For “CoPol & CrossPol”scans, the far field pattern shown in FIG. 7 is updated after each scanshift displaying the Co-Pol far field pattern each time. For circularlypolarized scans the far field display will only be updated after thesecond scan shift.

After a scan is complete, all the appropriate data are saved in thefolder named by the user from the LabVIEW Panel. If the folder alreadyexists, the user will be prompted to enter a new folder name before datacan be saved. All data files are saved in matrix form with eachhorizontal data point delimited by a tab. This allows the data to beread easily into a spreadsheet.

Obviously, the relative sizes and locations of these panels in thewindow is arbitrary and can be changed in accordance with the needs andthe preferences of the user.

A more detailed analysis can be made of the graphs shown in FIGS. 5, 6,7 and 8 from the Graph & Analysis button located at the bottom of theLabVIEW Panel shown in FIG. 4. This option displays a menu for the userto choose which folder contains the data. When a properly formattedfolder is chosen, the menu reads the polarity of the data from thecontents of the folder and displays a list of graphs available forviewing. The number of different data files for plotting range fromthree to six, depending on the scan polarity. For example, a “CoPolOnly” scan will contain the near field magnitude, near field phase, andfar field data matrices for plotting. However a “CoPol & CrossPol” willcontain both magnitude and phase for each near-field scan and a Co-Polfar-field pattern along with a Cross-Pol far-field pattern. The softwaredetermines the polarity that the data folder contains and only allowsthe user to choose graphs appropriate for that scan.

When a data folder is chosen, a variety of graphs can be selected forviewing. Each data file can be viewed in four different formats. Theseformats are 3D, H-Cut, V-Cut, and Contour. The 3D graph option shows thedata in 3 dimensional space allowing the graph to be rotated for viewingit at different angles. The H-Cut will show the horizontal cut of thedata with respect to the probe station beginning from left to right,whereas, the V-Cut will show the vertical cut of the data with respectto the probe station from top to bottom. Finally, the contour willdisplay the magnitude of the data as if it were viewed directly fromabove the probe station. It is displayed through shadowing where lightershades represent a higher value and darker shades represent lowervalues.

Each of the 3D graphs viewed in FIGS. 5, 6 & 7 is given a folder nameand graph type displayed in the caption of the window as well as beingdisplayed above the graph. Each graph also contains a series of menusdepending on the type of graph being displayed.

Every graph contains a File menu. Inside the File menu are four options.These options are Open, Save as Image, Print, and Close.

The Open option will redisplay the graph menu and allows the user toopen any new graphs they choose.

The Save as Image option will save the current screen shot of the graphto a bitmap image in the corresponding data folder for that graph.

The Print option writes the graph to a printer.

Finally, the Close option exits out of that single graph window. Eachgraph contains a Graph menu. Depending on the data being displayed andgraph type, the Graph menu includes different options. Each Graph menu,however, will at least contain the Add Cursor option. When selected, acursor will be added to the graph at the maximum value which can bedragged around to different data points on the graph. The graph titlewill also change to include the coordinates of the cursor.

For data other than near field phase, the user has the option to findthe peak of the graph. This can be done by selecting Find Peak in theGraphs menu. When this is chosen the cursor is moved to the graph's peakand the position is reflected in the graph's title.

Contour graphs of the type shown in FIG. 8 contain additional featuresfrom the other three graph types. The contour graph can display both thesurface in shades representing different point values and also in theform of contour lines. In the Graph menu the user can choose See ContourLevels and the graph will be transformed from surface shading to contourlines. When the graph is in the contour line display, the menu optionwill change to See Contour Surface and can be transformed back to thesurface plot through this new option. The data represented by the graphwill dictate the spacing of these contour lines. If these contour linesare too crowded or not sufficient, the user can add and remove contourlines as needed. When the graph is in Contour-Level mode, two newoptions are displayed in the Graphs menu. These are Add Contour Leveland Remove Contour Level.

For far-field patterns, the −3 dB contour line is displayed in red. Fromthe Add Contour Level menu option, contour lines of any value (to thetenths decimal position) can be added to the graph in any color chosenby the user.

The user can enter the contour level to add to the graph along withadjusting the color of the contour level by sliding the scroll bars onthe right corresponding to the colors red, green, and blue. The colorbox indicates the current color chosen by the user. The screen defaultsat black which is when all three scroll bars are positioned to the farleft. By scrolling the color bars to the right, the color of the contourlevel will contain more of that corresponding color. For example, for agreen contour level, the red and blue scroll bars should remain to thefar left while the green scroll bar is slid to the far right. Along withadding new contour levels a user can remove any existing contour levels

Each existing contour level is listed in a drop-down menu. The usershould select the contour level to be removed and click OK. Only onecontour level can be removed at a time, but there's no limit to how manycontour levels must be displayed on a graph.

Another option in the Graph menu is the Remove Grid option When gridlines are removed for better visibility, this option will be changed toRestore Grid, so the user has the option to restore the grid lines backonto the graph.

The cursor option can be used in both the surface and contour parts ofthe contour display. When switching between surface and contour lines,the cursor will be removed and the user can add the cursor again tocontinue using it. The cursor will not necessarily be added in the samespot it was before the graph transitioned from surface to contour linesor vice versa.

Far-Field Graphs

Far-field graphs differ from the near-field graphs in several ways.First, all the near-field graphs contain the same size data matrix.However, far-field data matrix sizes are defined by the FF Resolutionand the MATLAB transformation of the near-field data to far-field data.The FF Resolution input on the LabVIEW panel allows the user to decideon the size of the matrices to use in the far-field transformation. Thenear-field data will consist of part of this matrix padded with 0severywhere else. When the transformation occurs, the entire matrix isanalyzed and unrealistic data is removed. In this case, unrealistic datawould be data points where theta exceeds 90 degrees. These two factorsdetermine the size of the far-field data matrix. Another differencebetween far-field plots and near field plots are the x-, and y-axes. Innear-field graphs these axes are defined by the physical space scannedabove the antenna. In far-field graphs there are two possible displays.The default display is in theta-phi space. Phi and theta are sphericalcoordinates attempting to be displayed on a Cartesian graph. This isaccomplished by visualizing from above, the hemisphere that makes up thephi-theta plot. Phi remains the same starting at 0 degrees pointingdirectly right from the center of the plot and theta is displayed as theradius from the center of the graph. This can be visualized by imagininga hemisphere laying flat on a plane. The phi-theta combinations that liealong the hemisphere will be pulled directly down onto the plane belowthe hemisphere. The z-axis represents the normalized power in dB at eachphi-theta point on the plane. This representation causes the graph totake on a circular form limited by the fact that theta (the radius)cannot be larger than 90 degrees.

The other coordinate system that far-field graphs can be displayed in isU-V space. All far-field graphs have an extra menu option called Convertto UV Space found in the UV-TP Space menu, unique to far-field graphs.This transforms the graph from theta-phi space to U-V space. While thegraph is in U-V space, the menu option becomes Convert to TP Space whichallows the graph to be transformed back to theta-phi space. U-V space isan imaginary space used in the calculation of near-field data tofar-field data and is familiar to those in the antenna patterndiscipline. All the other graph features can be run in U-V space in thesame manner as in the theta-phi space.

Raw Data vs. Graphed Data

The coordinate system for transforming near-field data to far-field datauses the upper-left point as the origin with the x-axis pointing downand the y-axis pointing across. Therefore, a far-field transformation ofthese data will display the data as if viewed at a 90 degree clockwiseshift from the direction the data are scanned. However, to keep the datadisplay as simple as possible, this software rotates the data back tothe same orientation being scanned on the probe station. This isimportant if raw far-field data are to be used later.

Each scan folder contains these files:

-   Graph_Parameters.gd—This is information needed for the graphing    feature. If this file is removed or altered, the graphing features    in LabVIEW may not work.-   Experiment Parameters.rtf—This is a text files saved in the “Rich    Text File” format. This file displays all the parameters used when    the scan was conducted, along with any user comments entered in the    “comment box” before the scan,-   theta.psd—The theta values corresponding to each far-field data    point.-   phi.psd—The phi values corresponding to each far-field data point.-   u.psd—The u values corresponding to each far-field data point.-   v.psd—The v values corresponding to each far-field data point.

The different polarization files are described below:

-   CoPol Only—CoPol_Magnitude.psd—The Near-Field Magnitude of the    Co-Pol Scan.    -   CoPol_Phase.psd—The Near-Field Phase of the Co-Pol Scan.    -   CoPol.psd—The Co-Pol Far-Field Pattern.    -   CoPol_Real_Data.psd—The real data of the Co-Pol Scan.    -   CoPol_Imaginary_Data.psd—The imaginary data of the Co-Pol Scan.-   CrossPol Only—CrossPol_Magnitude.psd—The Near-Field Magnitude of the    Cross-Pol Scan.    -   CrossPol_Phase.psd—The Near-Field Phase of the Cross-Pol Scan.    -   CrossPol.psd—The Cross-Pol Far-Field Pattern.    -   CrossPol_Real_Data.psd—The real data of the Cross-Pol Scan.    -   CrossPol_Imaginary_Data.psd—The imaginary data of the Cross-Pot        Scan.-   CoPol & CrossPol—CoPol_Magnitude.psd—The Near-Field Magnitude of the    Co-Pol Scan.    -   CoPol_Phase.psd—The Near-Field Phase of the Co-Pol Scan.    -   CoPol.psd—The Co-Pol Far-Field Pattern.    -   CoPol_Real_Data.psd—The real data of the Co-Pol Scan.    -   CoPol_Imaginary_Data.psd—The imaginary data of the Co-Pol Scan.    -   CrossPol_Magnitude.psd—The Near-Field Magnitude of the Cross-Pol        Scan.    -   CrossPol_Phase.psd—The Near-Field Phase of the Cross-Pol Scan.    -   CrossPol.psd—The Cross-Pot Far Field Pattern.    -   CrossPol_Real_Data.psd—The real data of the Cross-Pot Scan.    -   CrossPol_Imaginary_Data.psd—The imaginary data of the Cross-Pol        Scan.-   LH Circular—x_Magnitude.psd—The Near-Field Magnitude of the x scan.    -   x_Phase.psd—The Near-Field Phase of the x scan,    -   x_Real_Data.psd—The real data of the x Scan.    -   x_Imaginary_Data.psd—The imaginary data of the x Scan,    -   y_Magnitude.psd—The Near-Field Magnitude of the y scan.    -   y_Phase.psd—The Near-Field Phase of the y scan.    -   y_Real_Data.psd—The real data of the y Scan.    -   y_Imaginary_Data.psd—The imaginary data of the y Scan.    -   LH_Circullar.psd—The LH Circular Far-Field pattern.-   RH Circular—x_Magnitude.psd—The Near-Field Magnitude of the x scan.    -   x_Phase.psd—The Near-Field Phase of the x scan,    -   x_Real_Data.psd—The real data of the x Scan.    -   x_Imaginary_Data.psd—The imaginary data of the x Scan.    -   y_Magnitude.psd—The Near-Field Magnitude of the y scan.    -   y_Phase.psd—The Near-Field Phase of the y scan.    -   y_Real_Data.psd—The real data of the y Scan.    -   y_Imaginary_Data.psd—The imaginary data of the y Scan.    -   RH_Circular.psd—The RH Circular Far-Field pattern.

The near-field to far-field transformation is implemented by the probestation near-field scanner.

Assuming that the probe is a perfect linear antenna, the total aperturefield measured by the probe can be represented in the coordinate systemshown above as follows:

Ē _(a)(x,y)=E _(ax)(x,y)î _(x) +E _(ay)(x,y)î _(y)  (1)

where, E_(ax)(x,y) the complex field measured with the probe oriented inthe î_(x) direction and E_(ay)(x,y) the field measured with the probeî_(y) directed. This expression is valid for any antenna, regardless oforientation or polarization, inasmuch as the total vector field issimply resolved into two orthogonal components. Obviously if a singlescan is used to obtain aperture field data, the field of the orthogonalpolarization is assumed to be zero.

Using the magnetic field equivalence principle, the far zone radiationfield of this aperture field can be expressed as:

Ē(θ,φ)=E _(θ)(θ,φ)î _(θ) +E _(φ)(θ,φ)î _(φ)  (2)

with

$\begin{matrix}{E_{\theta} = {\frac{j\beta}{4\pi}\left\lbrack {{P_{x}{\cos (\varphi)}} + {P_{y}{\sin (\varphi)}}} \right\rbrack}} & (3) \\{E_{\varphi} = {\frac{j\beta}{4\pi}{{{\cos (\theta)}\left\lbrack {{P_{y}{\cos (\varphi)}} + {P_{x}{\sin (\varphi)}}} \right\rbrack}.}}} & (4)\end{matrix}$

The terms,

P _(x)(u,v)=∫_(s) ∫E _(ax)(x′,y′)e ^(jw′) e ^(jw′) dx′dy′  (5)

P _(y)(u,v)=∫_(s) ∫E _(ay)(x′,y′)e ^(jw′) e ^(jw′) dx′dy′  (6)

are Fourier Transform integrals in the variables,

u=β sin(θ)cos(φ)  (7)

v=β sin(θ)sin(φ)  (8)

with

$\beta = {\frac{2\pi}{\lambda}.}$

The integration is performed over the surface S, which is defined by thelimits of the scan plane. These integrations are the basis of thenear-field to far-field transformation. Note, in this application, theintegrations of Equations (6) and (7) are performed with the twodimensional Fast Fourier Transform (FFT) routine provided in MATLAB. TheFFT requires that the number of sample points be a power of 2. Since, ingeneral, the number of data points from the test will not be a power of2, the data set is augmented by zeros to meet the FFT criteria. Inaddition to providing the increased computational speed of the FFT,augmentation increases the resolution of the function in the transformdomain. The probe station software utilizes this property by allowingthe user to set the resolution of the far-field pattern in the setupscreen. Effectively, when a resolution is selected, the total number ofpoints used in the FFT is chosen.

The Fourier Transform relationship is obtained through the variablesubstitutions defined in Equations (7) and (8). Thus the aperture fieldis transformed by Equations (5) and (6) to a space defined by the rangeof (u,v). The transformation can be visualized in this space and thisoption is provided by the Probe Station Near-Field Scanner Software.

The (u,v) space results from mathematical convenience and has to beconverted to (θ,φ) in order to visualize the field in real space. Whenconverting to (θ,φ), points where

$\theta > \frac{\pi}{2}$

are disregarded. This limitation is imposed by the magnetic equivalencetheorem which assumes the aperture field exists in an infinite plane anddoes not radiate in the region where z<0. The Probe Station Near-FieldScanner Software provides a number of graphing options to visualize thefield in (θ,φ) space.

The form of the far-field electric field, shown in Equations (3) and(4), is appropriate for apertures in a conducting ground plane. Forapertures in free space, the field is more accurately given by A.Ludwig, “The Definition of Cross Polarization”, IEEE AP-S January 1973,pp 116-119.

$\begin{matrix}{E_{\theta} = {\frac{j\beta}{4\pi}{\frac{1 + {\cos (\theta)}}{2}\left\lbrack {{P_{x}{\cos (\varphi)}} + {P_{y}{\sin (\varphi)}}} \right\rbrack}}} & (9) \\{E_{\varphi} = {\frac{j\beta}{4\pi}{{\frac{1 + {\cos (\theta)}}{2}\left\lbrack {{P_{y}{\cos (\varphi)}} + {P_{x}{\sin (\varphi)}}} \right\rbrack}.}}} & (10)\end{matrix}$

In general, any component of the far-field can be displayed by using theequation,

E _(display)(θ,φ)= E (θ,φ)·î _(d)  (11)

where î_(d) is a unit vector in the direction of the desired component.In the most general sense, the user can be allowed to choose thecomponent of the field however the software provides the most commonlyused components. For example, to display the {circumflex over (θ)}component, î_(d)=î_(θ) is used in Equation (11).

The co-polarized field and the cross-polarized field are computedfollowing the third definition provided by Ludwig (supra). Thisdefinition states that the reference direction of the polarization(Co-Pol) is that direction a far-field probe must match at θ=0 in orderto receive maximum power. For the Co-Pol pattern, this probe must matchand maintain the relationship with {circumflex over (θ)} and {circumflexover (φ)} at all angles. Similarly, Cross-Pol pattern is obtained byusing a unit vector orthogonal to the Co-Pol vector.

For a linearly polarized AUT, the co-pot direction depends on theorientation of the AUT. So for an AUT with a polarization angle that isoriented at an angle β to the {circumflex over (x)} axis,

î _(d) =î _(co)=cos(φ−β)î _(θ)−sin(φ−β)î _(φ)  (12)

and

î _(d) =î _(cross)=sin(φ−β)î _(θ)−cos(φ−β)i _(φ).  (13)

Because the probe that is used with the Probe Station Scanner is alinearly polarized waveguide, a circularly polarized AUT requires twoscans. The second scan must be done with the probe rotated 90° from thefirst. The right hand and left hand polarized components of the fieldare constructed from using the unit vectors

$\begin{matrix}{{{\hat{i}}_{d} = {{\hat{i}}_{rh}^{*} = {\frac{1}{\sqrt{2}}\left( {{\hat{i}}_{x} - {j{\hat{i}}_{y}}} \right)^{*}}}},} & (14) \\{and} & \; \\{{\hat{i}}_{d} = {{\hat{i}}_{lh}^{*} = {\frac{1}{\sqrt{2}}{\left( {{\hat{i}}_{x} - {j{\hat{i}}_{y}}} \right)^{*}.}}}} & (15)\end{matrix}$

The conjugate is used because the field to be shown would be the fieldreceived by an ideal circularly polarized antenna located at thefar-field point. Note that to actually perform the dot product withthese vectors, the far-field has to be transformed to a rectangularcoordinate system.

Finally, co-polarized and cross-polarized fields for circularpolarization can be determined through the use of the unit vectors,

$\begin{matrix}{{\hat{i}}_{d} = {{\hat{i}}_{co} = {\frac{1}{\sqrt{2}}\left\{ {{\left\lbrack {{\cos (\varphi)} + {^{- {j\delta}}{\sin (\varphi)}}} \right\rbrack {\hat{i}}_{\theta}} - {\left\lbrack {{\sin (\varphi)} - {^{- {j\delta}}{\cos (\varphi)}}} \right\rbrack {\hat{i}}_{\varphi}}} \right\}}}} & (16) \\{{\hat{i}}_{d} = {{\hat{i}}_{cross} = {\frac{1}{\sqrt{2}}{\left\{ {{\left\lbrack {{\cos (\varphi)} - {^{- {j\delta}}{\sin (\varphi)}}} \right\rbrack {\hat{i}}_{\theta}} - {\left\lbrack {{\sin (\varphi)} + {^{- {j\delta}}{\cos (\varphi)}}} \right\rbrack {\hat{i}}_{\varphi}}} \right\}.}}}} & (17)\end{matrix}$

The sense of the polarization is selected using

δ=π/2 Left Handed Circular Polarization, and δ=−π/2 Right HandedCircular Polarization.

While the invention has been described in combination with specificembodiments thereof, there are many alternatives, modifications, andvariations that are likewise deemed to be within the scope thereof.Accordingly, the invention is intended to embrace all such alternatives,modifications and variations as fall within the spirit and scope of theappended claims.

1-14. (canceled)
 15. A computer readable program stored in a tangiblemedium, said program comprising instructions for producing a grid workpattern of near-field signals radiated from a miniature antenna and forcharacterizing the far-field behavior of the antenna based upon thecaptured signals, comprising: a. A management software package havingthe keyed-in capability of controlling other embedded software packages;b. An embedded software package that is controlled by the managementsoftware package and that is useful in mathematically performing anear-field to far-field transform; and c. A visual software package thatis controlled by the management software package and that has thecapability of displaying near-field phase and magnitude plots and forshowing three dimensional, contours, vertical cuts and horizontal cutsthrough the far-field pattern distribution of the antenna based upon thetransforms performed by the mathematical software package.
 16. Thecomputer readable system according to claim 15 wherein the managementsoftware package includes a screen, means for the entry of scanparameters, including grid pattern to be used for taking a plurality ofnear-field measurements using a RF scanning probe, for moving saidscanning probe to each measurement location within the grid, and fortaking and recording each measurement.
 17. The computer readable systemaccording to claim 15 wherein the medium is selected from the groupconsisting of a floppy disc, a compact disc, a hard disc, a RAM a RUM,and combinations thereof.
 18. A software system for capturing thenear-field power performance characteristics of a miniature antenna, fortransforming the near-field characteristics to far-field properties, andfor displaying the near-field and far-field performance patterns,comprising: a. A management software package having the keyed-incapability of controlling other embedded software packages; b. Anembedded software package that is controlled by the management softwarepackage and that is useful in mathematically performing a near-field tofar-field transform; and c. A visual software package that is controlledby the management software package and that has the capability ofdisplaying near-field phase and magnitude plots and for showing threedimensional, contours, vertical cuts and horizontal cuts through thefar-field pattern distribution of the antenna based upon the transformsperformed by the mathematical software package.
 19. The software systemaccording to claim 18 wherein the management software package includes ascreen for the entry of scan parameters including a grid pattern, forinputting the linear and rotational movement patterns of the scannerprobe within the grid, for taking and recording each measurement, andfor determining the status of the scan.
 20. The software systemaccording to claim 18 wherein the mathematical software package utilizesa two dimensional fast Fourier equation to make the transform.